The present invention relates to a rotary magnetic head which comprises a pair of cylinders facing with an interval and forming a chamber therebetween; a rotating shaft projecting substantially coaxially with cylinders into the cylinders; a rotor having a pair of magnetic heads having a gap of predetermined length at the end thereof and mounted on shaft in the chamber of the cylinders; and a rotary transformer for coupling the magnetic heads to an external circuit.
A rotary magnetic head of the aforementioned type is already used in a video tape recorder and hence a VTR widely. In the VTR in general, a magnetic tape is fed obliquely on the outer peripheral surface of cylinders, and records and reproduces an electric signal while slidably moving with the magnetic head feeding along the surfaces of the cylinders while rotating. This scanning type is normally called "a helical scanning type", and the VTR employing this scanning type is excellent, but as the VTRs prevail, it is further desired to unveil a VTR which can further record and reproduce for longer time with light weight. For that purpose, it is desired to propose a rotary magnetic head having a small size, e.g., less than 50 mm in diameter and high accuracy as well as an adaptability for a mass production.
In order to clarify the features of the rotary magnetic head according to the present invention, a conventional rotary magnetic head will be first described. FIGS. 1 through 3 show the essential part of the conventional rotary magnetic head. A rotary magnetic head 20 has upper and lower cylinders 21 and 22, a slit 23 formed between the cylinders 21 and 22, and a magnetic tape (not shown) is fed slidably with the outer peripheries of the cylinders 21 and 22. A chamber 24 is formed between the cylinders 21 and 22, a rotating shaft 25 coupled with an external unit (not shown) is journaled with the lower cylinder 22 to extend into the chamber 24, and a rotor 26 is mounted at the extending part. The rotor 26 has a head base 27, magnetic heads 28, a mounting member 30 for mounting the magnetic heads 28 at the head base 27, and a rotary unit 32 for a rotary transformer 31. The magnetic heads 28 are so mounted substantially at equal distance from the center of axis of the rotating shaft 25 with the ends directed outwardly on a rectilinear line passing through the center of axis of the shaft 25.
FIG. 3 shows the magnetic heads 28. The magnetic heads 28 have a head core 28c bonded with a gap 33 of prescribed length G of head core halves 28a and 28b (FIG. 3), and head coils 28d are wound on the head core 28c.
As shown in FIG. 1, a rotary side core 32a forming the rotary unit 32 of the rotary transformer 31 and as shown in FIG. 2 two rotary side coils 32b are mounted at the head base 27, and a stationary side core 34a forming a stationary unit 34 of the rotary transformer 31 and two stationary side coils 34b are mounted inside the upper cylinder 21.
A magnetic tape (not shown) is fed along both the cylinders 21 and 22 in a spiral form, and the magnetic heads 28 are driven by the shaft 25 and are rotated. The ends of the magnetic heads 28 having a gap 33 are projected slightly from the slit 23, are slidably contacted with the magnetic tape while rotating, the magnetic heads 28 are coupled to an external circuit (not shown) through the rotary transformer 31 and thus reads and/or writes a signal.
Since the rotary magnetic head thus constructed is mainly used for a VTR, it is so fabricated as to has a small size, high accuracy and high performance. That is, the machining accuracy and assembling accuracy of the respective parts forming the rotary magnetic head are required to be remarkably high.
The following matters are required particularly for the assembled rotary magnetic head:
That is, (1) the magnetic heads 28 are disposed substantially at 180.degree. away from each other (it is required in an error to be within 1') with respect to the axial line of the shaft 25 particularly at the gap 33 formed therebetween, are spaced substantially at equal distance from the axial line, and the depth of the gap 33 projected from both the cylinders 21 and 22 should be substantially equal, and (2) the rotary side core 32a, stationary side core 34a and the rotary side coil 32b, stationary side coil 34b of the rotary transformer 31 are coaxially disposed substantially with respect to the rotating shaft 25. It was, however, difficult to produce the rotary magnetic head of the conventional configuration in mass production while sufficiently satisfying the aforementioned various requirements. Because the rotor 26 should be fabricated by assembling the head base 27, the magnetic heads 28, the mounting member 30 and the rotary unit 32a separately manufactured to obtain the prescribed requirements. It is accordingly necessary to fabricate separately precisely the many parts and to accurately couple the parts so as to satisfy the above described requirements. The magnetic heads 28 of the many parts forming the rotary magnetic head 20 normally have 2 to 3 mm of lateral and longitudinal sizes and less than 1 mm of thickness of small size and highly precise accuracy as required, and are also limited strictly at the mounting error even when they are assembled with other members. Such small parts are delicate, it is not only necessary to pay special attention in their transportation and positioning, but also needed to carefully take care of machining and associating so as not to cause a deformation and/or damage. For the purpose of machining and assembling such parts as ready as possible, small-size and high accuracy machining jig and tool as well as assembling jig and tool including a microscope are normally employed, but even when such jig and tool are used, the positioning of the rotary side core 32 of the rotary transformer 31 and the adjustment of the interval of the gap 33 of the head cores 28c are delicate, and are not easy and are necessary to depend much upon skilled technicians to perform the works. Accordingly, the rotary magnetic head 20 employing the rotor 26 of the conventional type shown in FIGS. 1 through 3 is not proper for the mass production.